The Pentagon is the world's largest office building, and a virtually a city in itself.

Up to 13,000 people could be working on the original project at any one time, it was an enormous undertaking. The original plans called for only three floors, but the military was preparing for war after the attack on Pearl Harbor, and it was decided two more floors should be added. To conserve steel, they used concrete ramps instead of elevators and the outside walls were made of reinforced concrete.

Since five roads surrounded the site and building site was an odd shape , builders chose a five-sided building, which is how the Pentagon got its name.

The building consists of five concentric rings connected by ten corridors that run, like spokes, from the inner ring to the outer. Interior courtyards that provide light separate the rings.

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The corridors are a total of 17.5 miles long, while the building provides a gross floor area of 6,500,000 square feet. There are 3,800,000 square feet for offices, concessions, and storage. The five-sided center courtyard covers five acres. Due to its unique design it takes only seven minutes to walk between any two points in the building.

A shopping concourse, numerous snack bars, cafeterias, dining rooms, banks, a subway station, and a bus platform make the Pentagon "a city within a city."

The structure is supported by 41,492 concrete piles. There are five floors, plus mezzanines and basements. The building itself is 77 feet, 3.5 inches high. Each outside wall is 921 feet long.

More than seven acres of glass went into the 7,754 windows in the Pentagon. There are 16,250 light fixtures, with some 250 bulb replacements made each day. Over 200,000 telephone calls are made daily through phones connected by 100,000 miles of telephone cable. There are 7,000 electric clock outlets, 691 drinking fountains, 131 stairways, 19 escalators, 13 elevators, 672 firehouse cabinets, and 284 rest rooms.

Why So Many Bathrooms?

At the time of construction segregation was still the law of the land in Virginia. Construction engineers were directed to build the building in compliance with state segregation laws requiring separate washroom facilities. Although federal buildings are exempt from state and local law, the military went along with this state law. Even though the extra bathrooms were built, President Roosevelt had issued an executive order 8802 the previous June (which forbade any kind of discrimination against government workers) no “colored” or “white” signs were ever put on the doors. The Pentagon for a long time was the only building in Virginia where segregation was not allowed. To this day there are four large washrooms on each of the main hallways leading from the outer ring of the building to the inner—two for men, and two for women.

The Pentagon site covers a total of 583 acres, while the building itself sits on 29 acres. The Pentagon's sewage treatment plant and the heating and refrigeration unit each cover one acre. The parking lot is 67 acres and has spaces for 8,770 vehicles.